The main objective of this pilot study is to investigate the protein / peptide plasma profiles before and after treatment with a direct anti-Xa (activated Factor 10) in patients with non-valvular atrial fibrillation to better understand the mechanisms of action of these molecules and perform exploratory analyses concerning proteins whose concentrations change after starting treatment.

Inclusion Criteria:

• The patient was correctly informed about the study, its implementation, objectives, associated restrictions and patient rights
• The patient must have given his/her informed and signed consent
• The patient must be insured or beneficiary of a health insurance plan
• The patient is available for 1 month of follow-up
• The patient has non-valvular atrial fibrillation that was diagnosed within the last 3 months. Documentation of atrial fibrillation by a 12-lead ECG, an ECG rhythm strip, atrial fibrillation episode lasting at least 30 seconds.
• The patient has a CHA2-DS2-VASc score = 1, that is to say the presence of at least one of the following risk factors: (1) congestive heart failure or moderate to severe systolic dysfunction of the left ventricle; (2) history of systolic blood pressure> 160 mmHg; (3) diabetes; (4) history of ischemic stroke or systemic embolism; (5) vascular disease (myocardial infarction, arterial disease); (6) age > 65 years; (7) female.
• The patient will start Rivaroxaban (Xarelto®) at the Nîmes University Hospital

Exclusion Criteria:

• The patient is participating in another interventional study
• The patient has participated in another interventional study within the past three months
• The patient is in an exclusion period determined by a previous study
• The patient is under judicial protection, under tutorship or curatorship
• The patient refuses to sign the consent
• It is impossible to correctly inform the patient
• The patient is pregnant, parturient, or breastfeeding
• Presence of a mechanical heart valve or valve disease
• Patient who recieved another new direct oral anticoagulant other than Xarelto® in the previous three months

The study population consists of patients in the cardiology department at the Nîmes University Hospital with non-valvular atrial fibrillation and who are candidates for treatment with a direct oral anticoagulant: Rivaroxaban (Xarelto®). Patients will be selected according to criteria designed to result in a homogeneous population (associated anticoagulants, etc., see below). For this study, patients must not have had a direct oral anti-Xa (activated Factor 10) in the 6 months preceding enrollment.